1. Field of the Invention
The present invention relates to magnetic detecting elements. Included among the material disclosed here are structures and techniques for magnetic detecting elements with an exchange bias system for controlling the magnetization of a free magnetic layer. Also included are discussions of a magnetic detecting element capable of improving reproduced output and suppressing the occurrence of side reading even with a narrower track, and of a method of manufacturing the magnetic detecting element.
2. Description of the Related Art
FIG. 24 is a partial sectional view of a conventional magnetic detecting element (spin-valve thin film element), as viewed from a side facing a recording medium.
In FIG. 24, reference numeral 1 denotes a first antiferromagnetic layer made of PtMn or the like, and a pinned magnetic layer 2 made of a NiFe alloy or the like, a nonmagnetic material layer 3 made of Cu or the like, and a free magnetic layer 4 made of a NiFe alloy or the like are formed on the first antiferromagnetic layer 1.
As shown in FIG. 24, second antiferromagnetic layers 5 are formed on the free magnetic layer 4 with a distance corresponding to a track width Tw apart in the track width direction (the X direction shown in the drawing), and electrode layers 6 are formed on the second antiferromagnetic layers 5.
In the magnetic detecting element shown in FIG. 24, an exchange coupling magnetic field is produced at each of the interfaces between the free magnetic layer 4 and the second antiferromagnetic layers 5 to pin the magnetizations in both end portions of the free magnetic layer 4 in the X direction. However, the central portion of the free magnetic layer 4 is weakly put into a single magnetic domain state to an extent which permits magnetic reversal in response to an external magnetic field. This method for controlling the magnetization of the free magnetic layer 4 is referred to as an “exchange bias system”.
The conventional example shown in FIG. 24 has a problem in which when the track width is further narrowed for increasing the recording density, a dead zone having a difficulty in magnetic reversal in response to an external magnetic field extends into the central portion of the free magnetic layer 4. This causes the problem of failing to achieve magnetic reversal in the central portion of the free magnetic layer 4 with high sensitivity to the external magnetic field, decreasing reproduced output.
The central portion of the free magnetic layer 4 is magnetized in the X direction by an exchange coupling bias magnetic field produced at each of the interfaces between both side portions of the free magnetic layer 4 and the second antiferromagnetic layers 5 due to an exchange interaction in the magnetic layer. The bias magnetic field is strongly exerted on the vicinities of the interfaces between the central portion and both side portions of the free magnetic layer 4, and the bias magnetic field can readily extend over the entire region of the central portion of the free magnetic layer 4 as the track width Tw decreases.
In the central portion of the free magnetic layer 4 strongly subjected to the bias magnetic field, magnetization is not pinned so strongly as in both side portions. Nonetheless, magnetic reversal can suffer a reduced sensitivity to the external magnetic field, thereby easily producing the dead zone in a region strongly subjected to the bias magnetic field. As a result, the reproduced output decreases as the track is further narrowed.
On the other hand, FIG. 25 is a partial sectional view of a conventional magnetic detecting element in which electrode layers 6 are formed in a different shape from the electrode layers 6 of the element shown in FIG. 24, as viewed from a side facing a recording medium. In FIG. 25, the same reference numerals as in FIG. 24 denote the same layers as the layers shown in FIG. 24.
Unlike in FIG. 24, in FIG. 25, the inner ends 6a of the electrode layers 6 in the track width direction (the X direction shown in the drawing) extend to the portions of the free magnetic layer 4 that are exposed in the distance T1 between the second antiferromagnetic layers 5, so that the track width Tw is regulated by the width dimension between the electrode layers 6 in the track width direction (the X direction).
In the conventional example shown in FIG. 25, the distance T1 between the second antiferromagnetic layers 5 in the track width direction can be increased, as compared with the conventional example shown in FIG. 24. In the conventional example shown in FIG. 25, magnetizations of both side portions of the free magnetic layer 4, which are formed in contact with the second antiferromagnetic layers 5 in the thickness direction, are strongly pinned in the X direction. On the other hand, in the intermediate regions of the free magnetic layer 4, which are formed by overlapping the inner ends 6a of the electrode layers 6 with the free magnetic layer 4, the strong bias magnetic field is exerted from both side portions of the free magnetic layer 4 to produce dead zones which substantially do not contribute to a change in magnetoresistance. Therefore, only the central portion of the free magnetic layer 4 is weakly put into a single magnetic domain state in the X direction, and thus the central portion becomes a sensitive zone in which magnetic reversal occurs with high sensitivity to the external magnetic field.
A sensing current from the electrode layers 6 to the free magnetic layer 4 mainly flows from the inner ends 6a of the electrode layers 6 to the central portion of the free magnetic layer 4, and thus the sensing current can be caused to flow less through the intermediate regions, i.e., the dead zones, of the free magnetic layer 4, thereby electrically killing the dead zones.
As described above, in the conventional example shown in FIG. 25, the distance T1 between the second antiferromagnetic layers 5 in the track width direction can be widened, as compared with the example shown in FIG. 24. Also, the track width Tw controlled by the electrode layers 6 can be matched with the width dimension of the sensitive zone of the free magnetic layer 4 apart from the dead zones. It is thus expected that a magnetic sensing element capable of producing great reproduced output even with a narrow track can be manufactured.
However, the conventional example shown in FIG. 25 also has a problem. Although the dead zones can assume a state in which they are electrically killed, they might not be completely magnetically killed, even though the intermediate regions of the free magnetic layer 4 are defined as the dead zones. In other words, although little magnetic reversal occurs in the dead zones in response to an external magnetic field, magnetization is not completely pinned. Thus, a little magnetic reversal can occur in response to the external magnetic field in some cases.
In this situation, the magnetic reversal is propagated to the central portion serving as the sensing zone in the free magnetic layer 4, and thus an external magnetic field entering in the dead zones is read as noise, deteriorating reproducing characteristics.
This situation results in a problem of side reading, in which the effective reproducing track width (which substantially corresponds to the track width Tw) becomes greater than the track width Tw (referred to as the “optical track width”) controlled by the electrode layers 6 shown in FIG. 25, thereby reading an external magnetic field leaking from an adjacent track on a medium. Therefore, the structure shown in FIG. 25 cannot realize a magnetic detecting element appropriately adaptable for a narrower track.
Particularly, the problem of side reading becomes significant as the overlap length between each of the inner ends 6a of the electrode layers 6 and the upper surface of the free magnetic layer 4 increases (i.e., as the width of each intermediate region in the track width direction increases).